astrophotography (level 1)

8/7/2019 Astrophotography (Level 1)

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Getting Started Guide to Digital Camera Astrophotography This guide is designed to begin discussion on this topic and not, yet, as the definitive reference. I hope that by combining all of our experiences, that we might create a document that would help beginners avoid allof the trouble that some of us have endured. This is our group’s document and is meant to help people newdigital camera astrophotography. You might notice some of your advice in this document. That is becauseit was good advice!

Familiarize yourself with the manual modes of your digital cameraTry taking pictures in a dark room of LEDs or other small lights. Next, try takingterrestrial pictures at night in your backyard. Make a habit of "bracketing" yourexposures.

Bracketing exposures is the practice of taking the same photograph with smallmodifications in exposure settings. For example, one might set the aperture to agiven setting and take pictures using several different exposure times.

Alternatively, one can set an exposure time and take a range of different aperturesettings. When set to manual modes, some cameras will indicate which aperture

and/or exposure time settings the camera would pick if it had been set to automaticmode. This is useful for providing a good starting point about which to bracket yoursettings.

Next, take pictures of the night sky using a tripod, or by placing the camera on atable or other sturdy surface. Conjunctions of the planets and/or the Moon areexcellent subjects for the digital camera.

If you have a wide-angle lens try photographing constellations, and if you have afish-eye lens try shooting an all-sky photograph or two.

Remember that you will not be able to see your camera in the dark so getting toknow the camera and its settings is an important prerequisite.

Shoot the MoonThe Moon is a lit subject and many have photographed it in Full Auto mode withoutany special settings, or capabilities. This is a good place to start. Its bright, big andbeautiful and you can test many different aspects of your equipment setup on thissubject. Many first astrophotography experiences begin with holding the camera upto the eyepiece and shooting pictures of the Moon.

The best time to photograph the Moon is not during a full Moon. Instead, try quartersor even smaller phases, as these will provide stunning details along the areabetween shadow and light. Experiment using your camera’s zoom, try to photographthe Moon completely, and then try to get close-ups of just craters.

Shooting the Sun is also fun and easy, provided you have the specialized filtersrequired to view the Sun. ***Never use a camera or telescope to photograph or viewthe Sun without the proper filter ***

Shooting the Moon and the Sun are rewarding and have provided the groundwork formost amateurs’ interest in digital camera astrophotography. An amateur can producenice quality images using just a hand-held camera, but when progressing to othersmaller or dimmer targets, having a mounted camera can help improve your results.



Connect the camera to the TelescopeMany DCA's (digital camera astrophotographers) have had good luck with a tripod orother bracket that fixes the digital camera on or just above the eyepiece, but mostuse some sort of digital camera adapter that attaches the camera to the eyepiece.

In our bookmark’s section there are many links to sites that have adapters that willallow you to connect your camera to your telescope. A couple of factors should betaken into consideration when deciding on the right connector; namely, thesturdiness of the physical connection and vignette avoidance.

Vignetting causes your photos to look as though they were taken in a tunnel. Tryyour connection in the daytime and check various zoom settings and note wherevignetting begins and ends. In general, the camera lens should be as close theeyepiece as possible. Also, to minimize vignetting, the aperture should be wideopen. When taking astrophotographs, cameras will often open the aperture to themaximum degree due to low light conditions, so this is less of an issue under thesecircumstances.

However, with bright targets (such as the Moon or the Sun with a solar filter), orwhen experimenting with manual aperture settings, the aperture may not always beopen to its full size. Since vignetting also depends on your equipment and level of magnification, even with a not-fully-opened aperture you may not experiencevignetting. But, if it is an issue when your aperture is not fully open, it may bebetter to modify settings to a more open aperture and shorter exposure times.

Many telescope to digital camera adapters/connections are sensitive to the weight of the camera and this sensitivity causes the subject to fall below the field of view of the camera. This is especially true if you are using a Barlow and/or Diagonal.

The effect of this problem is that the subject will be centered in the eyepiece butwhen the camera is attached, the subject will fall off the bottom of the field. To testthis, first target a bright star or planet and then, attach the camera and make surethat the subject is in a similar location in the camera’s LCD screen. If the subjecthas moved, try moving the subject to the top of the eyepiece, or simply position theobject using your camera.

When using a wedge or equatorial system, a diagonal should not be used. It justadds more stuff between the CCD and the subject and may cause field problemsdescribed above.

If your telescope is not mounted for astrophotography using a wedge, or equatorialsystem, be very careful about leaving the camera attached while slewing. You can

mangle your camera or other gear by slewing toward the zenith with the cameraattached. You may have to use a diagonal when photographing subjects near thezenith.



Find and track your subjectDue to the rotation of the earth, many objects will move out of your field of viewbefore you can shoot. Depending on their location in the celestial sphere, and yourcamera's exposure setting, you can accidentally blur a shot.

If you are using a telescope with a "Goto" computer or equatorial platform, use

them, as this will help with both finding and tracking your subject. If your “Goto” computer has a sync or high precision mode, this can also help.

If you own a star charting or planetary program, use this to determine where yoursubject will be in the sky and in relation to any obstacles in your viewing area. Notethe times when the object will be in the best location based on your site and its lightpollution. In highly light polluted sites, subjects are best viewed directly overheadwhile subjects located between 60° and 80° from the horizon are the easiest to viewand photograph.

Focus, Focus, FocusThere are many tricks to getting good focus and the basic rule of thumb is to set

your digital camera to manual focus at infinity and use your telescope to focus theimage. Many times the LCD display on your camera is less than perfect for this.

Many digital cameras have a separate viewfinder that does not look down the actuallens and therefore it cannot be used. The viewfinder in this case will show you alovely view of the back of your telescope.

If your digital camera has a video out port, you can attach this to a separate largervideo monitor. If your camera will show what it is about to shoot or has just shotthrough the computer interface, then a laptop or other computer may be helpful toprovide a larger image.

Both of these things wreck your night vision and are unpopular at star parties. Youcan use red rubylith foil to cover the monitor’s screen, which will reduce the amountof white light emitted, and this will help in keeping your night vision. A small pieceof the rubylith for your camera’s LCD might also be in order.

Specialized devices have been created to assist with focusing in traditional and CCDastrophotography and may prove helpful with digital cameras. One trick to focusingbright stars or planets is to use a Hartmann mask.

A Hartmann mask is a disk that fits over the business end of your telescope, like it’sdust cap, which has holes cut into it. These are available commercially or can bemade from foam core board. Using the mask, a bright star or planet will appear asmultiple images, one for each hole, when out of focus and one image when in focus.This is normally much easier to see than the focus of a single image. To focusdimmer subjects try focusing on a bright star in the same constellation.

Most consumer digital cameras have a digital zoom feature that can be the absolutebest focusing tool. Simply, center the subject and then zoom in all the way,centering as you go, until a star or planet feature fills your primary viewer. Now, asbefore, use the telescope to focus image. Once the image is focused back out of thedigital zoom before taking the picture. In addition, increasing the ISO setting justduring focusing for dim subjects can be very helpful in some cameras.



Noise ReductionA consumer digital camera uses a charge coupled device or CCD to produce images.An astronomical CCD camera uses similar technology but adds cooling to the CCD toreduce noise. Without the cooling, all long exposure photographs taken with digitalcameras will contain noise. Depending on your subject, great care will need to betaken to eliminate this noise. Bright subjects such as The Moon, Sun, and planets

may not exhibit noise but dim subjects such as deep space objects will alwaysrequire intervention.

Put your camera’s lens cap on and try taking the longest exposure possible with yourcamera. Now examine the image. See that it is not black but instead full of tinystar clusters…well almost…it is just noise.

To keep your background black and your stars real, you should take some dark fieldframes before each camera setting adjustment. Once you have a subject in the fieldof view and focused, you should take a few “dark” field frames by putting thetelescope’s cap on and shooting at the same exposure as planned for the subject.

This will only work if your telescopes dust cap is “light tight.” If it is not light tightuse a dark cloth or simply use your camera’s lens cap.

Allow the camera’s CCD to cool down before each dark field image and if possibletake dark frames and normal frames with the LCD turned off. Write down orotherwise record the subject, exposure, and dark frame file numbers or names.Later on, we will use these to subtract out any hot pixels or other noise caused bythe long exposure.

Many different image-processing packages include the ability to remove noise byusing image mathematics to subtract the dark frames from the images. Multipledark frames can be averaged to provide more productive noise reduction and it isgood to take more than one dark frame, anyway, in case something happens to one

frame you will have a back up.

By examining dark frames from a night’s astrophotography session, you should startto see patterns in the noise. Some of these are defects or “hot pixels” and bynoticing their location you can try and place subjects in “hot pixel” free zones infuture sessions.

If your digital camera has a noise reduction feature built-in to the camera try takingshots with and without the noise reduction on. Those without will need dark framesas suggested above but those with the noise reduction on will already be darksubtracted by the camera. We have found that this noise reduction works for somesubjects and cameras very well and for others not as well as doing the darksubtraction manually.

Stacking and integrationJust as a larger aperture telescope collects more light, multiple subsequentphotographs, combined, can also collect more light. Because most digital camerascannot take very long exposures, most are less than 16 seconds and many are lessthan 60 seconds, combined subsequent images can simulate extended exposures. Inaddition, stacking brings out details in bright subjects such as planets, in fact, mostsuccessful planet photographs contain 20 to 30 images stacked.



Begin by taking multiple exposures with the camera at the same settings. Thenumber of exposures depends on the subject and can vary from two to themaximum possible with your memory card or even multiple memory cards.

Stacking can be done with standard image processing software but is usually easier

with software made for astronomical purposes. The main reason for this is thatearth is still moving throughout your astrophotography session and the images arenot all aligned especially those at the beginning and at the end the of session.Astronomical image processing software usually has an alignment or registrationfunction to properly align the images before stacking them.

It is best to shoot each shot within a minute of the next if you are interested instacking.

ShootingAt this point, you have found your subject, focused the image, and taken your darkframes. You are also prepared to shoot multiple images of the same subject so thatthey may later be stacked.

To obtain the most detail it is advised to use the finest or maximum non-interpolatedresolution available in your camera. Having said this, your memory card will fill veryquickly using this resolution and processing of your images will take longer.

To start with, you might want to try using the second best resolution and then, afteryou have had a chance to familiarize yourself with the process, upgrade to thehighest resolution.

It is recommended that you shoot a single subject per session so that the images arenot confused and so that you can spend ample time on each subject. Also observingis half the fun and if you spend all of your time in the dark holding your shutterrelease, you will be missing a very important part of astronomy.

Remember to document each exposure noting the settings and subjects. If yourcamera automatically documents your photos then you do not need to writeeverything down. Be sure to put each subject in a separate album or write downwhich photos go with which subject, if you do happen to shoot more than onesubject.

Also, do not forget to turn off the LCD monitor while taking any exposures.

It is important to have darks that exactly match the normal images so if you changeanything be sure to shoot more darks to match the new settings.

If your computer is close, run in and look at the images, during the middle of yoursession, and check the images to make sure that all is well. It may be possible tocorrect the problem and salvage the session or you might see some detail or otherarea of interest that should be exploited. In either case, a quick peek every so oftencan never hurt.



Image ProcessingWe have completed all of our shots and packed up the telescope and all of ourvarious gear. Our astrophotography session is complete…or is it?

Take the camera in the house and look at the pictures. Not a pretty site, are they?The key to good astrophotography of any kind is image processing and the key to

almost any astrophotography with digital cameras is image processing.

First, go to bed. It is enough to spend the night in the backyard taking the shots,wait until the next day or even the next cloudy night to begin the image processingof your photographs.

Transfer the images from your camera to your computer under a folder with today’sdate and organize them so that the dark frames, and normal images of similarexposure, or other settings are grouped together in additional subfolders. Renamethe dark frames as dark1, dark2 etc. and normal frames as subject1 thru subject15i.e. M13-1, M13-2.

Begin by inspecting the images for out of focus or other problem images and movethese to a folder named Problems.

Here is an example folder structure:

My Astro Photos08232001

MarsDark1.jpgDark2.jpgMars1.jpgMars2.jpgMars3.jpg

Mars4.jpgProblems

DC23197.JPG

The first task is dark subtraction. If you have multiple “dark” frames, then each of these can be averaged (or use median) to create a master dark image.

Next, take your dark or master dark and subtract it from each of your normalimages. This process can be found in the image math section of some imageprocessing software or in the calibration or correction section of astronomical imageprocessing programs.

Lets try dark subtraction in Paint Shop Pro 7. We open the dark frame and we opena normal image. We select image menu then Arithmetic and are presented with adialog box, which has two pulldowns for the two images. The operation we areinterested in is subtract and PSP7 defines subtract as Image1 – Image2 so we selectour dark frame in the image 2 pulldown and our normal image in the image 1pulldown. We check the All channels checkbox so that we get a color result, leavethe other settings alone, and press ok. A new dark subtracted image pops up infront with a lot less noise! You can leave the dark image and repeat for each normalimage.



Now that your images have been dark subtracted, they can be stacked to providemore detail and simulate longer exposures.

Lets try stacking the images in Astrostack. Using PSP (it can do this in bulk) oranother program we must convert the JPG or TIF format images to Windows Bitmap(BMP) format before they can be loaded into Astrostack.

In Astrostack, click the BMP button and it prompts you to select the first BMP imageand then the last image. This means the files should be numbered as describedabove as Mars1, Mars2, Mars3, and Mars4 and we would select Mars1 for the Firstand Mars4 for the last.

Once selected, Astrostack will load the BMPS and stack them. We should also selectAlign Auto and click GO to register the stacked images. In the result window, we seethe stacked image. We can perform a number of other operations from Astrostackbut for now, we can click save result and then exit.

We just stacked 4 images of Mars into a single hopefully more detailed image. Wecould also have automatically dark subtracted the images by clicking the correctbutton and selecting the dark frame.

Astronomical Image processing is a topic worthy of its own guide and there are manyadditional processing functions that can help to make your images the best that theycan be.

For example, an un-sharp mask, a low pass filter, and convolution/de-convolutionalgorithms can really bring out the detail and suppress unwanted background orother artifacts.

It might seem obvious, but using paint functions to create features and otherfabrication practices are generally frowned upon in the astronomy community.

Finally, share your images with this group and othersThat is one of the best parts of this exciting endeavor, sharing images (even badones) with the group. You can gain perspective and insight while learning what to dothe next time the clouds part for you. Above all, have fun.

Links[ digital_astro ] is a yahoo group for people interested in Digital CameraAstrophotography. Be sure to visit the files and bookmarks section.http://yahoogroups.com/group/digital_astro

The Digital Camera Astronomical Imaging FAQ prepared by Simon Szykman contains

frequently asked questions and answers that should be used as a companion to thisdocument.http://users.erols.com/szykman/Astro/AstroDigiCamFAQ.html

Ckcpower is a digital camera and accessories company that specializes in connectingyour camera to your telescope.http://www.ckcpower.com/



Digi-T by Scopetronix is a digital camera to telescope adapter. Scopetronix hasmany other ways to connect your camera to your telescope.http://www.scopetronics.com/digitalcam.htm

TeleVue now has a new line of Digital Camera adapters to fit its excellent line of eyepieces.

http://www201.pair.com/resource/astro.html/regular/products/tele-vue-optics/digital.camera.to.eyepiece.html

William Optics has a revolutionary new 1¼ 28mm eyepiece that is threaded andmade to connect a Nikon Coolpix camera to your telescope. Rumor has it thatadditional cameras will be added in the future.http://www.buytelescopes.com/product_details.asp?pNumber=3940

Mediachance has many different free software programs for digital cameraphotography and the “blackframe” and “hotpixels” programs are perfect for digitalcamera astrophotography.http://www.mediachance.com/digicam/blackframe.htm

Paint Shop Pro, an inexpensive but powerful general graphics program with a 30-daytrial, which has many advanced features including Arithmetic options, which areperfect for Color dark subtractions of Digital Camera images. Price is $99USdownload.http://www.jasc.com/products/psp/

AstroStack, a freeware astronomical image-processing program, will do darksubtraction and stacking and other functions all at once and is a good way to getstarted with image processing. To use this program the images must first beconverted to BMP format and reduced in size by either cropping or resizing.http://utopia.ision.nl/users/rjstek/english/software/index.htm

Cadet, another freeware astronomical image-processing program, is more complexbut provides advanced functionality not found in other freeware programs. To usethis program images must be also be converted to BMP and then colored images splitinto their red, green, blue, and optionally luminosity components.http://www.terra.es/personal2/oscarcj/introeng.htm

Iris, also free, is an astronomical image-processing program with a command lineinterface that can be saved as a script for batch processing. This software is byChristian Builhttp://www.astrosurf.com/buil/us/iris/iris.htm

GIMP, freely distributed general public licensed image processing program, has manyimage processing functions.http://www.gimp.org/

Astronomical Image Processing for Windows is an excellent book by Richard Berry etal that also includes AIP4WIN a powerful astronomical image processing program.The book is available from Willmann Bell for $79US.http://www.willbell.com/aip/index.htm



** CAUTION: Observing the Sun is the one and only thing in astronomythat can be really dangerous. If the filter falls off your scope forsome reason, you will instantly damage your eye, which might not berepairable. Always double-check everything before observing the Sun.Especially make sure that the filter cannot fall off your scope, or be

blown off by wind. Secure it tightly. Remember to cover any finder onyour scope too. Many people have the habit to look thru their finderscope without thinking about it. This can seriously damage your eyes ifthe scope is directed at Sun. It might be a good idea to find anexperienced solar observer near you and let him introduce you to this.Take extra care if kids are around. TAKE CARE ALWAYS.

astrophotography (level 1)

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